1. Field of the Invention
The present invention relates to an optical apparatus having a temperature compensating function, and more particularly, to an optical element position correcting device, a focusing device or a lens barrel arranged, for example, to automatically correct changes in focus by correcting changes in position of a lens or a like optical element caused by temperature variation.
2. Description of Related Art
Many of low-priced cameras, particularly, fixed focus cameras, recently marketed are provided with built-in lens units which are composed of molded lenses or combinations of glass lenses and molded lenses, instead of glass lenses.
In cases where a lens unit includes a molded lens, however, the shape and refractive index of the lens tend to be changed by temperature variation. The image forming position of a lens unit of such a kind shifts forward in a low temperature environment and backward in a high temperature condition, thereby causing a deviation in focus. To solve this problem, in the case of the lens barrel which has a focus driving means and causes the focus driving means to draw out a photo-taking lens unit in the direction of an optical axis so as to adjust focus, the temperature of environment is detected by a temperature sensor disposed within the camera body, and a focus deviation resulting from temperature variation is corrected by changing the amount of drawing-out of the photo-taking lens according to the environment temperature detected.
In the case of the lens barrel having no focus driving means, a focus deviation due to temperature variation is corrected by stopping down a maximum diaphragm aperture.
A zoom lens barrel disclosed in Japanese Laid-Open Patent Application No. HEI 5-236322 is arranged to move an image sensor which is provided for converting a focused image into an electrical signal in the direction of an optical axis according to temperature variation, so that a sharply focused image can be obtained at the time of zooming. In the case of such a zoom lens, the image sensor is secured to a holding member which is arranged in a hat-like sectional shape to expand or contract in the direction of the optical axis according to temperature variation, and the holding member is secured to the body of the lens barrel.
A lens barrel disclosed in Japanese Laid-Open Patent Application No. SHO 60-194416 is arranged to correct focus deviations due to temperature variation as follows. Expansion or contraction of the lens barrel in the direction of its optical axis caused by temperature variation is mechanically detected. The mechanical change detected is optically converted into an amount of optical displacement. Then, a focusing lens is moved with a motor in such a way as to cancel out the amount of optical displacement.
Further, in an arrangement disclosed in Japanese Laid-Open Patent Application HEI 8-15595, the movement of a long bar which extends in the direction of an optical axis and is arranged to elongate and contract according to temperature variation is transmitted to an arm by utilizing leverage. The arm then causes the position in the direction of the optical axis of a condenser lens to vary in the direction opposite to the elongating direction of the bar in such a way as to correct the focus position of the condenser lens.
However, the conventional arrangement mentioned above has presented the following problems. In the case of the lens barrel having a focus driving means, it is necessary to have a temperature sensor arranged to detect environment temperature. The use of the temperature sensor, however, not only causes an increase in cost but also results in a complex structural arrangement for control over a lens unit drawing-out action.
As for the lens barrel having no focus driving means, the F-number of the lens becomes a darker F-number, because the full-open (maximum) aperture of its diaphragm is stopped down, as mentioned above.
The zoom lens barrel disclosed in Japanese Laid-Open Patent Application No. HEI 5-236322 is arranged to correct a focus deviation at the time of zooming by moving the image sensor in the direction of the optical axis to correct an image forming position where a back focal distance is changed by expansion and contraction of the lens barrel body due to temperature variation. If the lens unit of the zoom lens barrel is a lens unit composed of molded lenses, however, the focus of the lens unit would be caused to deviate by changes in shape and refractive index of the lens unit resulting from changes of environment temperature.
The lens barrel disclosed in Japanese Laid-Open Patent Application No. SHO 60-194416 is arranged to correct focus deviations due to temperature variation by carrying out feedback control as follows. Expansion or contraction of the lens barrel in the direction of its optical axis due to temperature variation is mechanically detected. The mechanical change thus detected is converted into an amount of optical displacement. The focusing lens is driven and moved by the motor to cancel out the optical displacement. Adoption of this arrangement, however, results in a complex structure of the lens barrel.
In the arrangement disclosed in Japanese Laid-Open Patent Application No. HEI 8-15595, the movement of the long bar which extends in the direction of the optical axis and elongates or contracts according to temperature variation is transmitted to the arm by utilizing leverage. The focus position obtained by the condenser lens is corrected by varying the position in the direction of the optical axis in the direction opposite to the elongating direction of the bar. This arrangement, however, not only makes the structure of an optical apparatus complex but also does not apply to a case where the lens position is to be shifted for correction in the elongating direction of the bar.